This invention relates to a self-tracking sensor suspension mechanism for use with smart pipeline inspection gages, commonly termed xe2x80x9csmart pigsxe2x80x9d, used in the inspection of pipelines. The sensor suspension mechanism improves the data gathering capabilities of pigs in the presence of varying conditions of the surfaces being inspected. Although the invention is most applicable to the interior inspection of pipelines, it is also susceptible to other applications, including inspection of tank interiors.
In-line inspection tools, or xe2x80x9csmart pigsxe2x80x9d as they are commonly referred to are used to gather information with respect to the condition of a pipeline through which the pig is propelled. Pigs are also used to perform more simple tasks such as cleaning of pipelines; however, the term xe2x80x9csmart pigxe2x80x9d implies a tool for performing a more complex task. This includes use in the measurement of metal loss due to corrosion, cracks due to stress corrosion, pipeline deformity, and the like.
A smart pig is typically propelled along the pipeline under pressure or pressure difference of the pipeline fluid. The pipeline fluids may be gas, liquid, or a combination of both. A smart pig that is introduced to a pipeline having an appropriate pressure differential and volumetric flow rate will be propelled at the same rate as the fluid.
The primary purpose of smart pigs is to determine the amount of metal loss or removed metal in the pipeline. Metal loss may occur as a result of corrosion on the inside or outside of the pipe. It may also occur as a result of gouging of the pipeline exterior as a result of third party damage. The industry standard for measuring metal loss is the use of Magnetic Flux Leakage (MFL). Other techniques, such as acoustics, are also used.
In obtaining data from within the pipeline, such as MFL data, the smart pig will have a mechanism for propelling it down the pipeline, typically a tractor, and means for magnetizing the pipeline wall, typically called a magnetizer. In addition means are provided to sense MFL and for powering the data acquiring components of the smart pig. Likewise, means for storing the gathered data will be provided.
The sensors used for measuring the MFL signal are positioned radially in spaced apart relation about a body portion of the magnetizer of the smart pig. The suspension mechanisms typically used for mounting the sensors to the body portion of the magnetizer include the cage type, the parallel suspension type and the single arm type.
With the cage type the sensor mechanism is maintained against the pipe wall through the use of links and springs. This mechanism allows the sensor to adjust for varying wall thicknesses of the pipe. Slots are provided at each end of a head to which the sensor is connected to enable them to tilt relative to one another. This type mechanism works very well in smooth pipe where there are no dents, large welds or other protuberances along the pipe wall. In the event of a significant protuberance, however, the sensor lifts off the pipe wall and the measuring of the MFL signal is degraded.
The parallel suspension type consists of a four bar linkage mechanism. The linkage mechanism allows the sensor to traverse the pipe inner surface during movement parallel to the pig axis. The sensor carrier, in this case a magnetizer, has means of support that urges its axis parallel to the nominal axis of the pipe. With this arrangement, the sensor is connected to the links and is maintained against the pipe wall during passage of the pig through the pipeline. As with the cage type these devices are spring-loaded to urge the sensor toward the pipe wall. This type of suspension has the same disadvantage as discussed above with respect to the cage type. Rocking of the sensor carrier also results in movement of the sensor relative to the pipe inner surface thus degrading the measurement of the MFL signal.
A third type suspension mechanism is designated as the single arm type. In this device a single arm is pivotally connected at one end to the body portion of the pig. A spring urges the opposite end containing the sensor against the pipe wall during travel of the pig through the pipeline. This mechanism has a disadvantage that depressions on the surface being inspected tilts the sensor away from the surface to degrade the MFL signal. In addition any rocking motion of the pig during travel through the pipeline causes the sensor to correspondingly tilt to degrade the signal.
It is accordingly a primary object of the present invention to provide a self-tracking sensor suspension mechanism for use with smart pigs that overcomes the difficulties of prior art devices, as discussed above, to improve the quality of inspection and specifically the quality of a MFL detected signal.
An additional object of the invention is to provide a self-tracking sensor suspension mechanism for use with smart pigs that functions to hold a sensor or sensors at a selected orientation, which may be parallel, perpendicular or angular, relative to a surface being inspected, and particularly the inner surface of a pipe, regardless of surface irregularities.
In accordance with the invention, a self-tracking sensor suspension mechanism for use with a pig traveling through a pipeline is provided. The pig includes a body portion to which a plurality of self-tracking sensor mechanisms are attached. Each of these mechanisms has a link pivotally attached to the body portion of the pig at one end of the link. Means are provided for urging the link in a direction away from the body portion of the pig. A trailing arm is pivotally connected at one end thereof to the link. Means are provided for urging the trailing arm in a direction away from the body portion. A sensor is embedded within or connected to the surface portion of the trailing arm for contact with a pipeline interior surface when the pig is traveling within the pipeline.
The means for urging the link in a direction away from the body portion of the pig may be a spring, as may be the means for urging the trailing arm in a direction away from the body portion.
The link may be pivotally attached to the body portion by a pin extending through the link at the end thereof attached to the body portion.
The trailing arm may be pivotally connected to the link by a pin extending through the link and the trailing arm.